There is an ongoing concern in the tobacco industry to produce cigarettes having wrappers which reduce the ignition proclivity of the smoking article, or the tendency of the smoking article to ignite surfaces which come into contact with the lit smoking article. Reports have been made of fires attributed to burning cigarettes coming into contact with combustible materials. A justifiable interest exists in the industry to reduce the tendency of cigarettes, or other smoking articles to ignite surfaces and materials used in furniture, bedding, and the like upon contact.
Thus, a desirable feature of smoking articles, particularly cigarettes, is that they self-extinguish upon being dropped or left in a free burning state on combustible materials.
It has long been recognized in the tobacco industry that the cigarette wrapper has a significant influence on the smolder characteristics of the cigarette. In this regard, various attempts have been made in the art to alter or modify the cigarette wrappers in order to achieve the desired tendency of the cigarette to self-extinguish, or in other words to reduce the ignition proclivity characteristics of cigarettes.
The prior art describes the application of film-forming solutions to cigarette paper to reduce the paper permeability and control the burn rate. It has been shown that when these materials have been applied in discrete areas along the length of the cigarette, the cigarette shows a reduced propensity to ignite a substrate, tends to self-extinguish, and has a higher puff count.
U.S. Pat. No. 5,878,753 to Peterson and U.S. Pat. No. 5,820,998 to Hotaling, et al. which are incorporated herein by reference, for example, describe a smoking article wrapper being treated with a film-forming aqueous solution to reduce permeability. U.S. Pat. No. 5,878,754 to Peterson which is also incorporated herein by reference describes a smoking article wrapper being treated with a non-aqueous solution of a solvent soluble polymer dissolved in a non-aqueous solution to reduce permeability.
Although some improvements have been made in the art, there is still a need for an improved method for producing a cigarette wrapper with reduced ignition proclivity properties. Specifically, a need exists for an improved method of applying a film-forming solution to a paper wrapper in discrete areas for decreasing the permeability of the wrapper down to a desired range, especially when the wrapper has an initially high porosity.
The present invention is generally directed to paper wrappers for smoking articles with reduced ignition proclivity and to a process for making the wrappers. For example, in one embodiment, the process includes the steps of providing a paper wrapper made from a paper web. For example, the paper wrapper can contain flax fibers, softwood fibers, hardwood fibers and mixtures thereof. The paper wrapper can also include a filler, such as calcium carbonate, in an amount from about 10% to about 40% by weight.
A film-forming composition is applied to the paper wrapper at particular locations. The multiple layers of the film-forming composition form treated discrete areas on the wrapper. The discrete areas are separated by untreated areas. The treated discrete areas have a permeability within a predetermined range sufficient to reduce ignition proclivity. For example, the treated areas can reduce ignition proclivity by reducing oxygen to a smoldering coal of the smoking article as the coal burns and advances into the treated areas.
In accordance with the present invention, the film-forming composition contains a film-forming material. The film-forming material has a relatively low viscosity which typically indicates a lower molecular weight. By using a film-forming material having a relatively low viscosity, the film-forming composition can have a higher solids content and yet have a solution viscosity capable of being used in conventional application techniques, such as being used in a gravure printing process.
For example, the film forming material contained within the composition can have a viscosity of less than about 500 cP when present in a 3% aqueous solution at 25xc2x0 C. More particularly, the film-forming material can have a viscosity of less than about 250 cP at the above conditions, particularly less than about 100 cP at the above conditions, and in one embodiment, at a viscosity of about 20-60 cP at the above conditions.
The solids content of the film-forming composition can be at least 6% by weight, particularly at least 10% by weight, and more particularly in an amount from about 10% to about 20% by weight. The film-forming material can be, for instance, an alginate, such as sodium alginate. It should be understood, however, that various other film-forming materials can be used. Other film-forming materials that are believed to be useful in the present invention include guar gum, pectin, polyvinyl alcohol, cellulose derivatives such as ethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch, and starch derivatives.
The viscosity of the film-forming composition can vary depending upon the manner in which the composition is applied to the paper wrapper. For most applications, however, the viscosity of the film-forming composition should be at least 250 cP, particularly at least 500 cP, more particularly at least 800 cP, and in one embodiment at a viscosity of at least 1000 cP or greater at 25xc2x0 C. The composition can have a pH of below about 8.0, such as below about 7.5. For example, the pH of the composition can be from about 4 to about 7.5. In one embodiment, the film-forming composition can be heated in order to lower the viscosity of the composition as it is being applied to the paper wrapper.
The film-forming composition can be can be applied to the paper wrapper according to various methods. For example, the composition can be printed onto the paper using, for instance, flexography, direct gravure printing, and offset gravure printing.
In one embodiment, the discrete areas formed by the film-forming composition are in the shape of circumferential bands disposed longitudinally along the smoking article. The bands can have a width of greater than about 3 mm, such as from about 4 mm to about 10 mm. The bands can be spaced from each other at a distance of from about 5 mm to about 50 mm and particularly from about 10 mm to about 40 mm.
The amount of the film-forming composition that is applied to the paper wrapper depends upon the particular application and various factors. For example, the film-forming composition can be applied to the wrapper in an amount from about 1% to about 30% by weight based upon the weight of the wrapper within the treated areas, and particularly in an amount from about 2% to about 20% by weight.
Once applied to the paper wrapper, the treated areas can have a permeability of less than about 40 Coresta, particularly less than about 30 Coresta, and more particularly from about 5 Coresta to about 25 Coresta. The initial permeability of the paper wrapper can be from about 20 Coresta to about 90 Coresta or greater.
Other features and aspects of the present invention are discussed in greater detail below.